One of the most powerful tools of the radar engineer - and certainly the simplest - is a graphic device called the phasor. Though no more than an arrow, the phasor is the key to a nonmathematical understanding of a great many seemingly esoteric concepts encountered in radar work: the formation of real and synthetic antenna beams, sidelobe reduction, the time-bandwidth product, the spectrum of a pulsed signal, and digital filtering, to name a few. Unless you are already skilled in the use of phasors, don't yield to the temptation to skip ahead to chapters 'about radar.' Having mastered the phasor, you will be able to unlock the secrets of many intrinsically simple physical concepts which otherwise you may find yourself struggling to understand. This chapter briefly describes the phasor. To demonstrate its application, the chapter goes on to use phasors to explain several basic concepts which are, themselves, essential to an understanding of material presented in later chapters.